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Thread: Adjusting an ABV and measuring flow rates through the boiler

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  1. #1
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    Default Adjusting an ABV and measuring flow rates through the boiler

    With so much talk about OT and boiler condensing in other threads, I shifted my attention to the little spoken about 'guy', the Automatic Bypass Valve.

    In today's world of self modulating pumps, TRVs and zones, how does one set up the ABV?

    This is likely to become a topic as debated as "is balancing really relevant with TRVs and zones".

    Most boilers will specify a minimum flow rate. So how does one actually measure the flow rate running through the boiler.

  2. #2
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    Another interesting point.

    The Baxi HE boiler my sons has says no ABV required and no heatsink radiator required as long as th boiler controls the pump.

    But the boiler has no live feed, just switched from the zone valves as shown in yjr diagram in the manual.

    Can it really cope with no bypass at all?

    Tony

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    And why did British Gas install an ABV if none is required?

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    Quote Originally Posted by the crooner View Post
    And why did British Gas install an ABV if none is required?
    Probably best, they did. You can always turn the ABV down so that it never operates. But you cannot magic one in, if you need it.

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    Quote Originally Posted by bruce_miranda View Post
    Probably best, they did. You can always turn the ABV down so that it never operates. But you cannot magic one in, if you need it.
    Well, you can't completely disable them - most only let you set them as high as 0.6 bars differential pressure. You're unlikely to see this pressure if there is another relief valve somewhere though.

  6. #6
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    How does one measure flow rate through the boiler?

  7. #7
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    The technical data for my boiler shows the water displacement that the boiler pump can deliver for a 'particular resistance' of 910L/hr at 20C (max resistance 250mbars) with the boiler adjusting water flow until a temperature difference between flow and return water is reached that is acceptable for the control system is achieved.

    So what does all mean when setting the Honeywell ABV 145? The graph 'appears' to indicate that for a minimum flow of 910L/hr at 250 mbars, the valve should be set at about 3.

    Then again you could just do what this guy suggests from minute 7.00 onwards:

    https://www.youtube.com/watch?v=KfJ5SrBnoS4

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    Quote Originally Posted by HenGus View Post
    Then again you could just do what this guy suggests from minute 7.00 onwards:

    https://www.youtube.com/watch?v=KfJ5SrBnoS4
    LOL, well that is the worst ABV I think I have seen installed for a while! Think he needs a heating engineer out, as he seems to have left himself a leak on the pump valve (6:59).

    I personally also use mass flow rate calculation to work heating flow rates out...

    So the flow rate required in kg/second = H/TD*SH (H = heat required in Watts, TD = temperature drop of the system and SH = Specific heat capacity of the fluid (Water = 4187 joules)).

    Pub Question... If a boiler requires a minimum flow rate 1032 litres per hour with a 20 degrees C differential, what is its heat output in kW?

  9. #9
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    Quote Originally Posted by The EVOHOME Shop View Post
    LOL, well that is the worst ABV I think I have seen installed for a while! Think he needs a heating engineer out, as he seems to have left himself a leak on the pump valve (6:59).
    Could be worse... Could be that plumberparts doughnut.

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    Quote Originally Posted by Dan_Robinson View Post
    Could be worse... Could be that plumberparts doughnut.
    I was thinking of you and your shiny pipes when I watch that...

    Output in kW please...

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